1. Field of the Invention
The invention is directed to purified and isolated novel human IL-1 epsilon polypeptides, the nucleic acids encoding such polypeptides, processes for production of recombinant forms of such polypeptides, antibodies generated against these polypeptides, fragmented peptides derived from these polypeptides, the use of such polypeptides and fragmented peptides in cellular and immune reactions and as molecular weight markers, the use of such polypeptides and fragmented peptides as controls for peptide fragmentation, and kits comprising these reagents.
2. Description of Related Art
Interleukin-1 (IL-1) is a member of a large group of cytokines whose primary function is to mediate immune and inflammatory responses. There are five known IL-1 family members which include IL-1 alpha (IL-1α), IL-1 beta (IL-β), IL-1 receptor antagonist (IL-1ra), IL-1 delta (IL-1δ, as disclosed in PCT US/99/00514), and IL-18 (previously known as IGIF and sometimes IL-1 gamma). IL-1 that is secreted by macrophages is actually a mixture of mostly IL-β and some IL-1 α (Abbas et al., 1994). IL-1α and IL-1β, which are first produced as 33 kD precursors that lack a signal sequence, are further processed by proteolytic cleavage to produce secreted active forms, each about 17 kD. Additionally, the 33 kD precursor of IL-1α is also active. Both forms of IL-1 are the products of two different genes located on chromosome 2. Although the two forms are less than 30 percent homologous to each other, they both bind to the same receptors and have similar activities.
IL-1ra, a biologically inactive form of IL-1, is structurally homologous to IL-1 and binds to the same receptors. Additionally, IL-1ra is produced with a signal sequence which allows for efficient secretion into the extracellular region where it competitively competes with IL-1 (Abbas et al., 1994).
The IL-1 family ligands bind to two IL-1 receptors that are members of the Ig superfamily. IL-1 receptors include the 80 kDa type I receptor (IL-1RI) and a 68 kDa type II receptor (IL-1RII). The ligands also bind to a soluble proteolytic fragment of IL-1RII (sIL-1RII) (Colotta et al., Science 261(5120):472-75, 1993).
The major source of IL-1 is the activated macrophage or mononuclear phagocyte. Other cells that produce IL-1 include epithelial and endothelial cells (Abbas et al., 1994). IL-1 secretion from macrophages occurs after the macrophage encounters and ingests gram-negative bacteria. Such bacteria contain lipopolysaccharide (LPS) molecules, also known as endotoxin, in the bacterial cell wall. LPS molecules are the active components that stimulate macrophages to produce tumor necrosis factor (TNF) and IL-1. In this case, IL-1 is produced in response to LPS and TNF production. At low concentrations, LPS stimulates macrophages and activates B-cells and other host responses needed to eliminate the bacterial infection; however, at high concentrations, LPS can cause severe tissue damage, shock, and even death.
The biological functions of IL-1 include activating vascular endothelial cells and lymphocytes, local tissue destruction, and fever (Janeway et al., 1996). At low levels, IL-1 stimulates macrophages and vascular endothelial cells to produce IL-6, upregulates molecules on the surface of vascular endothelial cells to increase leukocyte adhesion, and indirectly activates inflammatory leukocytes by stimulating mononuclear phagocytes and other cells to produce certain chemokines that activate inflammatory leukocytes. These IL-1 functions are crucial during low level microbial infections. However, if the microbial infection escalates, IL-1 acts systemically by inducing fever, stimulating mononuclear phagocytes to produce IL-1 and IL-6, increasing the production of serum proteins from hepatocytes, and activating the coagulation system. It is also known that IL-1 does not cause hemorrhagic necrosis of tumors or suppress bone marrow stem cell division. Nevertheless, IL-1 is lethal to humans at high concentrations.
Given the important function of IL-1, there is a need in the art for additional members of the IL-1 ligand family. In addition, in view of the continuing interest in protein research and the immune system, the discovery, identification, and roles of new proteins, such as human IL-1 epsilon and its receptors, are at the forefront of modern molecular biology and biochemistry. Despite the growing body of knowledge, there is still a need in the art for the identity and function of proteins involved in cellular and immune responses.
In yet another aspect of the invention, the identification of the primary structure, or sequence, of an unknown sample protein is the culmination of an arduous process of experimentation. In order to identify an unknown protein sample, the investigator can rely upon a comparison of the unknown protein sample to known peptides using a variety of techniques known to those skilled in the art. For instance, proteins are routinely analyzed using techniques such as electrophoresis, sedimentation, chromatography, and mass spectrometry.
Comparison of an unknown protein sample to polypeptides of known molecular weight allows a determination of the apparent molecular weight of the unknown protein sample (T. D. Brock and M. T. Madigan, Biology of Microorganisms 76-77 (Prentice Hall, 6th ed. 1991)). Protein molecular weight standards are commercially available to assist in the estimation of molecular weights of unknown protein samples (New England Biolabs Inc. Catalog: 130-131, 1995; J. L. Hartley, U.S. Pat. No. 5,449,758). However, the molecular weight standards may not correspond closely enough in size to the unknown sample protein to allow an accurate estimation of apparent molecular weight. The difficulty in estimation of molecular weight is compounded in the case of proteins that are subjected to fragmentation by chemical or enzymatic means (A. L. Lehninger, Biochemistry 106-108 (Worth Books, 2d ed. 1981)).
The unique nature of the composition of a protein with regard to its specific amino acid constituents results in a unique positioning of cleavage sites within the protein. Specific fragmentation of a protein by chemical or enzymatic cleavage results in a unique “peptide fingerprint” (D. W. Cleveland et al., J. Biol. Chem. 252:1102-1106, 1977; M. Brown et al., J. Gen. Virol. 50:309-316, 1980). Consequently, cleavage at specific sites results in reproducible fragmentation of a given protein into peptides of precise molecular weights. Furthermore, these peptides possess unique charge characteristics that determine the isoelectric pH of the peptide. These unique characteristics can be exploited using a variety of electrophoretic and other techniques (T. D. Brock and M. T. Madigan, Biology of Microorganisms 76-77 (Prentice Hall, 6d ed. 1991)).
When a peptide fingerprint of an unknown protein is obtained, this can be compared to a database of known proteins to assist in the identification of the unknown protein (W. J. Henzel et al., Proc. Natl. Acad. Sci. USA 90:5011-5015, 1993; B. Thiede et al., Electrophoresis 1996, 17:588-599, 1996). A variety of computer software programs are accessible via the Internet to the skilled artisan for the facilitation of such comparisons, such as MultiIdent (Internet site: www.expasy.ch/sprot/multiident.html), PeptideSearch (Internet site: www.mann.embl-heiedelberg.de . . . deSearch/FR_PeptideSearchForm.html), and ProFound (Internet site: www.chait-sgi.rockefeller.edu/cgi-bin/prot-id-frag.html). These programs allow the user to specify the cleavage agent and the molecular weights of the fragmented peptides within a designated tolerance. The programs compare these molecular weights to protein databases' to assist in the elucidation of the identity of the sample protein. Accurate information concerning the number of fragmented peptides and the precise molecular weight of those peptides is required for accurate identification. Therefore, increasing the accuracy in the determination of the number of fragmented peptides and the precise molecular weight of those peptides should result in enhanced success in the identification of unknown proteins.
Fragmentation of proteins is further employed for the production of fragments for amino acid composition analysis and protein sequencing (P. Matsudiara, J. Biol. Chem. 262:10035-10038, 1987; C. Eckerskorn et al., Electrophoresis 1988, 9:830-838, 1988), particularly the production of fragments from proteins with a “blocked” N-terminus. In addition, fragmentation of proteins can be used in the preparation of peptides for mass spectrometry (W. J. Henzel et al., Proc. Natl. Acad. Sci. USA 90:5011-5015, 1993; B. Thiede et al., Electrophoresis 1996, 17:588-599, 1996), for immunization, for affinity selection (R. A. Brown, U.S. Pat. No. 5,151,412), for determination of modification sites (e.g. phosphorylation), for generation of active biological compounds (T. D. Brock and M. T. Madigan, Biology of Microorganisms 300-301 (Prentice Hall, 6th ed. 1991)), and for differentiation of homologous proteins (M. Brown et al., J. Gen. Virol. 50:309-316, 1980).
Thus, there also exists a need in the art for IL-1 polypeptides suitable for use in peptide fragmentation studies, for use in molecular weight measurements, and for use in protein sequencing using tandem mass spectrometry.